Copper bearing stainless steel



Aug. 14, 1945. R. THIELEMANN ,38 ,273

COPPER BEARING s'rAINfiEss STEEL Filed April 28, 1944 Inventor:

Rudolf" H.Thie| e ann,

His Attorney.

Patented Aug. 14, 1945 COPPER BEARING STAINLESS STEEL Rudolf H.Thielemann, Portland, reg., asslgnor to General Electric Company, acorporation of New York Application April 28,1944, Serial No. 533,163

(cut-P125) 1 claims.

The present invention relates to stainless steel and more particularlyto a modified stainless steel alloy containing copper and adapted foruse in gas turbines, axial flow compressors, jet propulsion apparatusand the like.

Heretofore the production ofsatisfactory compressor blades has been oneof the serious problems in connection with the manufacture of axial flowcompressors for gas turbines and jet-propulsion equipment. The number ofsuch blades employed in a compressor depends of course upon the size andcapacity of the compressor and may vary from about 500 to 2000 blades,one half of which are stationary and the other half rotary.

The shape and dimension of the blades tend to make them very difllcultto machine. In cross section the blades have an air foil shape and theyCarbon .12 max.

' Chromium 12-14 Tungsten 2.5-3.5 Manganese .50 max. Nickel 1.8-2.2Silicon .50 max. Phosphorus .025 max, Sulphur .025 max. Iron Balance areusually twisted about their longitudinal axis.

A dovetail structure is providedon one end of the blades so that theymaybe secured to a supporting member such asa rotary wheel or the like.The length or the blades vary from about one to eight or ten incheswhile the width may vary from something less than one inch up to abouttwo or three inches depending upon the design. The trailing'edge of theblade is very thin and for design reasons it is desirable to make thatedge less than .010" thick. Because or the complex shape and thinsection, it is desirable to make the blades by the lost wax or precisioncasting technique commonly employed in the manufacture of dentures andthe like.

The single figure of the drawing is a'perspective view of a compressorblade and support adapted for use in a gas turbine or jet propulsionapparatus. It comprises a blade I having an enlarged end 2 comprising adovetailed portion I whereby the blade may be secured to a suitablesupporting member 4. I

From a metallurgical point of view the blade material should be at leastsemi-stainless to resist rusting and corrosion. It should also have ahigh tensile strength, high elastic limit, good ductility, high fatiguestrength, high internal damping capacity, and should be readily mebutbecause of the high chinable. A steel having such properties may havethe following composition:

This steel composition is primarily a forging alloy and has desirableproperties in the forged and heat treated condition. However, it doesnot possess good casting properties; for example it has a high meltingpoint. is very sluggish and the thin edged blades can be cast only ifthe metal is preheated to temperatures of about 150 to 200 F. above itsnormal casting temperature. when this is done complete blades may becast, temperature employed the shrinkage is excessive. Also. the hotshrink causes defects in the castings and the percentage or rejectedcasting as a result of X-ray examination is very high. It maybe statedtherefore that it is practically impossible to successfully cast bladeshaving the above noted composition and employing precision castingtechnique.

In carrying out the present invention I employ a modified stainlessalloy having the following composition:

Carbon .10-.20 Chromium 12-14 Tungsten 2.5-3.5 Manganese -100 Silicon.20-.80 Nickel 1.8-2.2 Copper 5-8 Iron Balance except for normalimpurities.

' The preferred composition contains not more than .12% carbon. about13% chromium. about 3% tungsten, not more than .5 70 manganese, not morethan silicon, 2% nickel and 1% copper. Phosphorus and sulphur may bepresent in the alloy but should be kept as low as possible. For example,the alloy preferably should not con- .tain more than 025% phosphorus andnot more than 025% sulphur. My improved alloy has desirable fluidity andcasting properties and is particularly adaptedfor use in the precisioncasting process. One per cent of copper greatly increases the fluidityof the alloy and after a heat treatment at about 700 C. the alloy hasunusually high ductility and physical properties. While the usefulpercentage e of copper employed may vary from .5 to 3% an addition of 1%provides most satisfactory results. Additions above 1.5%

produces some precipitation hardening accom-. panied-by a reduction inductility. The follow-- lng table represents the physical properties ofthe alloy in the as-cast condition and after a heat treatment for twohours at 700 C.

After having been heat treated as indicated the cast blades are soductile that they can be sharply bent 90 or 120 without cracking.-

What I claim as new anddesire to secure by Letters Patent of the UnitedStates, is:

1. An alloy containing about .10 to .20% carbon, about 12 to 14%chromium, about 2.5 to 3.5% tungsten, about .20 to 1.00 manganese, .20to .80% silicon, about 1.8 to 2.2% nickel, about .5 to 3% copper, withthe remainder substantially all iron.

iron.

aseaers 2. An alloy containing about 13% chromium, about 3% tungsten.about 2% nickel and about 1%. copper and containing fractionalpercentages but not more than .12% carbon, not more than manganese, notmore than .50% silicon, not more than 025% phosphorus, and not more than025% sulphur, the remainder of the alloy being substantially all iron.

3. An alloyconsistinz of about .10 to 20% carbon, about 12 to 14%chromium, about 2.5 to

3.5% tungsten, about .20 to 1.00% manganese,

about .20 to 00% silicon. about 1.8 to 2.2% nickel, about .5 to 3%copper, the remainder being substantially all iron, said alloy havingbeen heat treated at a temperature of about 700 C. and slowly cooledtherefrom.

51. A process for heat treating an alloy consisting'oi about .10 to 20%carbon, about 12 to 14% chromium, about 2.5 to 3.5% tungsten, about .20to 1.00% manganese, about .20 to .80% silicon, about 1.3 to 2.2% nickel,about .5 to 3% copper, the remainder being substantially all iron, saidprocess comprising heating the alloy for about two hours at atemperature of about 700 C. and thereafter slowly cling the alloy.

5. A compressor blade for gas turbines. aui flow compressors, Jetpropulsion apparatus or the like, said blade comprising an alloycontainins .10 to 20% carbon, about 12 to 14% chromium, about 2.5 to3.5% tungsten, about .20 to 1.00% manganese, about .20 to silicon, about1.8 to 2.2% nickel, about .5 to 3% copper, the remainder beingsubstantially all iron.

0. A precision casting having the following composition: about .10io.20%carbon, about 12 .to 14% chromium, about 2.5 to 3.5% tungsten, about .20to 1.00% manganese, about .20 to .80%

silicon, about 1.8 to 2.2% nickel, about .5 to 3% copper, the remainderbeing substantially all '7. A precision cast alloy having the followingcomposition, about .10 to-.20% carbon, about 12 to 14% chromium, about2.5 to 3.5% tungsten, about .20 to 1.00% manganese, about .20 to .80%

' silicon, about 1.8 to 2.2% nickel, about'.5 to 3% copper, theremainder being substantially all iron,

, said casting having been heat treated at 700 C.

' RUDOLF H. THIELEMANN.

